The mechanisms by which herpesviruses mediate fusion and virus entry into the cell are almost certainly more complex than those of other families of enveloped viruses. While most enveloped viruses use a single viral glycoprotein complex and a single receptor for entry into a cell, the herpesviruses typically require multiple viral glycoprotein complexes encoded by multiple genes. While much remains to be learned about the mechanisms of entry for all herpesviruses, the gamma-2 herpesviruses are particularly lacking in specific, useful information in this regard. The gamma-2 herpesvirus of rhesus monkeys, rhesus monkey rhadinovirus (RRV), will be used as a model of human herpesvirus 8 (HHV-8;the Kaposi sarcoma-associated herpesvirus) to define the viral glycoproteins required for entry into different types of target cells and to define and to better understand the glycoprotein targets of the natural neutralizing antibody response. In the first specific aim, the RRV glycoproteins that are principally responsible for strain specificity of the neutralizing antibody response will be defined. These experiments will not only shed light on the major targets of the natural neutralizing antibody response, they will also allow us to determine whether glycoprotein sequences evolve with time of infection of a single individual as a consequence of selective pressure from neutralizing antibodies. In the second specific aim, the highly unusual codon usage of RRV gH and gL and the extreme dependence of gH and gL expression on Orf 57 will be explored in terms of the strategic advantage it may provide to the virus. Finally, the viral glycoproteins of RRV that are necessary and sufficient for entry into permissive fibroblasts, B cells, and endothelial cells will be defined. PUBLIC HEALTH RELEVANCE: The natural host immune response to human herpesvirus 8 (HHV-8) prevents the development of disease in most but not all cases. The proposed experiments will define the viral protein targets of the natural neutralizing antibody response and will provide insight into virus-host interactions using a relevant monkey model. The experiments will also facilitate use of HHV-8 as a vaccine or gene therapy vector.